This invention relates generally to contacts or pins constructed to be inserted through apertures in printed circuit boards and more particularly it relates to contacts having a split or sheared portion which forms a pair of offset legs which fit into, and grip the sides of, holes provided therefor in printed circuit boards.
The current use of terminal posts retained in apertures in printed circuit boards is quite extensive. For several years such retention has been accomplished by inserting a square post into a round aperture with the four edges of the post frictionally engaging the aperture walls. Such an arrangement presents several problems, with one of the most difficult being the small variation in hole size and pin size that can be tolerated, either with or without the use of solder. Without solder such variation of size usually cannot exceed an accumulation of more than two or three thousandths of an inch. Outside such tolerance limits the square post will either have insufficient retention force or literally fall out of the hole or, on the other hand, the force required to insert the post will be too large and sometimes destroy the walls of the aperture.
If solder is employed, contact must still be made between the edges of the post and the aperture walls in order for solder to flow thoroughly in-between the post and the aperture walls. If the post is too large, problems of high insertion force and damage to the aperture walls are present.
The problem attendant with inserting a square post in a round aperture has led to the development of other types of aperture engaging means. One such development employs a post having a portion which is compliant and can give as it enters the aperture, thereby permitting greater dimensional tolerances. In one form such compliant portion is split along the longitudinal axis thereof to form a pair of legs. The two legs are spread apart to form a configuration similar to that of an eye of a needle so that when they are inserted into the circuit board hole they act as a pair of oppositely bowed spring members and provide an outwardly directed force against the wall of the hole, thereby creating both an electrical contact and a mechanical friction fit with the wall of the circuit board aperture.
One difficulty with such a structure involves the amount of material in the legs, i.e., the maximum cross sectional area of the legs with respect to the size of the aperture in which the contact is to be inserted. More specifically, since the two legs are spread apart it is necessary that the aperture be of sufficient size to receive the legs and also to insure that the legs are not pressed together any farther than the original configuration of the flattened portion before the splitting thereof occurs. Further, the retention force between the legs and the aperture wall is limited by the resiliency of the legs as they are pressed together.
With such prior art structure the total cross-sectional area of the legs is relatively small compared with the hole size in the printed circuit board. Since it is usually desired to keep the holes in the printed circuit board as small as possible the legs will, in fact, have a correspondingly small cross-sectional area, thereby limiting the amount of spring and strength of said legs to a point where they are not practical unless they are soldered into the aperture.
The cross-sectional size of the legs could, of course, be increased simply by enlarging the circuit board hole. Such a solution, however, usually is unsatisfactory since space on a printed circuit board is limited. For example, pins on a printed circuit board are often spaced closely together in either a matrix or a row so that enlarging the holes would result in an undesired decrease of pin density.